1. Field of the Invention
This invention relates to power failure detection for computers and systems comprising computers. In particular, this invention relates to early detection of power loss for systems comprising personal computers.
2. Description of Related Art
It is known in the art of digital computer systems to provide for detection of power failure and to effect a response thereto. For large computer systems it is known to provide auxiliary sources of power generation to permit continued supply of power indefinitely in the event of loss of supply from the primary source. Conversely, for so-called “personal computers”, it is known to provide so-called un-interruptible power supplies that incorporate auxiliary power sources to permit temporary operation in the event of loss of power from the primary source. While the use of such power supplies insures adequate power to effect an orderly shut down of the computer, such power supplies add substantial cost. It is known in the art to monitor the outputs of a personal computer power supply to detect out of tolerance conditions typical of loss of power from the primary source. As loss of applied power to power supplies for personal computers will result in gradual decay of power supply outputs, it is known to inhibit certain operations of such computer components on detection of out-of-tolerance conditions of power supply outputs.
Of particular concern with respect to loss of power is the potential for corruption of data stored in non-volatile, re-writable memory. For purposes of this description, non-volatile, re-writable memory is a data retention facility in which data may be recorded and replaced in normal use, and wherein the recorded data will be retained indefinitely in the absence of supply of power from a source external to the facility. Known devices providing these capabilities include magnetic disk memories, optical disk memories, and non-volatile semiconductor memories. As power supply outputs decay, out-of-tolerance operating voltages can result in uncontrolled operation of such memory devices and corruption of data recorded therein. Of particular concern in this regard is the potential for corruption of operating system program data and the attendant inability to successfully restart the computer thereafter. Hence, there is a need to reduce or eliminate potential data corruption in the event of power failure without use of auxiliary power sources.